Machine tools of various types operate through a valving system which interacts with a pneumatic controlled clutch and/or brake assembly. For safety reasons, the control valves which are used to operate these machine tools require the operator to actuate two separate control signal applying contacts essentially simultaneously. This requirement of simultaneous application ensures that the operator will not have his hand near the moving components of the machine tool when an operating cycle is initiated. The two control signal applying contacts can then be connected to the valving system which allows compressed air to be delivered to the machine tool to perform its operating cycle.
Safety rules and regulations require the valving system to be designed such that if a component in the valving system malfunctions, the valving system will not allow additional movement of the machine tool. In addition, the valving system must ensure that a new operation cycle of the machine tool cannot be initiated after a component of the valving system has become defective.
Prior art electromagnetic valving systems which are utilized for the operation of machine tools meet these safety requirements through the use of a double valve assembly. The double valve assembly, includes two electromagnetic supply valves which are normally closed. Each of the supply valves is moved to an open position in response to an electrical control signal. The two supply valves are arranged in series with respect to the source of compressed air. The double valve assembly also includes two exhaust valves which are normally open. Each exhaust valve is closed by a respective supply valve when it is opened. It is therefore necessary for the supply valves to be opened simultaneously otherwise, supply air will be exhausted from the system through one of the exhaust valves. The opening and closing of the valve units is monitored by sensing air pressures in the respective valve units and then compare these two pressures. The monitoring and comparing of these two pressures is accomplished by using a single air cylinder which is separated into two chambers by a piston. The pressure in each valve unit is delivered to one of the chambers. Thus, unequal pressures in the valve units will cause movement of the normally static piston which will then interrupt the electrical signal to one of the valve units. This and other external electronic monitoring arrangements are expensive and require that electrical signal processing equipment be designed and utilized.
The continued development of the valving systems for machine tools has been directed toward more reliable, simpler and less costly valving systems which both meet and exceed the safety performance requirements in force today as well as those proposed for the future.
The present invention provides the art with a control valve system which operates entirely pneumatically thus eliminating the need for electrical monitoring and the associated controls. The control valve system includes a plurality of valves each of which open or dose during the actuation or deactuation of the valves. The control valve system monitors the dynamic movement of the various valves of the system to ensure the proper functioning of the control valve system. The control valve system moves to a locked out position upon sensing a malfunction and remains in this locked out position until a resetting operation is performed. Thus, the operation of the control assembly is totally dynamic and the system does not rely on the monitoring of a static member to ensure its proper function.
Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.